Actually, they do resist sewer gasses rather well. The device engineering is setup in such a way that sewer gas back pressure forces them to seal even harder. They only open when the "call" for air-behind-water is present. They have been in use in the USA for 25 years and 20 million have been installed. There is a divided opinion but AAV's are permitted by the Uniform Plumbing Code. Section 911.0 which allows the engineering of a vent system.

If you keep reading, there will still be some max distance from the nearest vent in the building. The problem with gas isn't that your valve leaks. It is lighter than air and will create pressure in the pipe, at some point it has enough pressure to burst thru the water in the trap.

Since we are on a main line, not a septic, I think the article you found is not applicable. Found a new manufacturer and they provided this pic. Notice they have applications for bath, sink and toilet. I will be calling them today to get more details.

The question becomes, height. When your valve open and allows air in as air is lighter than the gas it will follow the water down the pipe. So givin some time the gas will displace all the air in the pipe down to the next level where it can escape. If the distance down is 10 ft and you have a considerable amount of sq inches of gas pushing up. What is that pressure and how much pressure can the few inches of water in the sink trap hold back.

That is why I suggested reading further in the code. Write now your finding everything to back up what you want to do. You also have to put on a negitive hat so you can have a fair arguement with yourself.

AAVs are accepted by major model building and plumbing codes, including IRC 2003, for single or multi family residential construction, and by American Society of Sanitation Engineers (ASSE). However, some local code authorities may be unfamiliar with Air Admittance Valves or reluctant to accept them despite code listing. Prior to using an AAV, an installer should contact the local building code official for specific approval status. In the United States, one open-air plumbing vent per structure is required.

This all I have been able to find and it's someones opinion, but you might be allright

I am not totally sold on the AAV solution. There is a connection to the standard vent stack in the run ... but it is quite a way away, so I want to use the AAV to supplement the venting, not to completely substitute for it. Code DOES NOT allow the AAV to be the only vent access in the waste run.

We have not opened the walls yet, so I have to wait for that to take measurements. Will brief you along the way as the project develops. Since this is an historic structure, we cannot add new vent stacks to the roof line ... worse, the exterior walls are filled concrete block, making pipe runs very difficult.

When something is close to code, it's not about the inches to make it code, it's more important to understand what problem the code is trying to solve and then see if you are in fact solving that problem. Good luck, historic stuff is worst.